Prättigau and Davos
Westliche Silvretta
Avalanche Problems
Persistent weak layers
1
Field notes
Persistent Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary are very challenging to recognise. Distinctive noise (resembling a “whumpf” sound) occurring when a weak layer beneath a slab collapses. The air of the weak layer is forced outside the snowpack, with the resulting whumpf sound being heard. The sound usually indicates an unstable situation and can be accompanied by surface cracking. A whumpf is a clear avalanche alert.EAWS glossary sounds and shooting cracks are typical when present, but you can have a serious weak layer with no warning signs at the surface. Knowledge of how the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has evolved is essential. SLF's travel advice is direct: travel conservatively, avoid terrain where the consequences of being caught are large, and treat the history of weather and snow as more important than what you can see today. Read the full bulletin.
Snowpack & Weather
Snowpack
In Lower Valais, northern Valais and the Bernese Oberland, there is as much snow at high altitudes as usual for this time of year, but less in the other regions. There is particularly little snow on the southern flank of the Alps and at intermediate altitudes on the eastern part of the northern flank of the Alps.
Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary are located in particular on northern and eastern slopes above approximately 2400 m. Hardly any avalanches have been triggered in the last four days, except in southern Lower Valais. Here, human activity triggered isolated avalanches in the weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary.
Below approximately 2800 m, the surface of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is stable on very steep southern slopes, otherwise it is mostly brittle. On northern slopes, the snow is sometimes looser and faceted at high altitudes. Below approximately 2100 m, the snowpack beneath the Layer of hard-compacted snow resulting from a melt-freeze process; increases firmness.EAWS glossary is saturated. Wet and gliding avalanche activity has decreased appreciably. Isolated wet snow slides and gliding avalanches are possible with the sunshine and rising temperatures during the daytime.
Weather review for Saturday
Conditions were sunny and mild in the mountains.
Fresh snow
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Temperature
At midday at 2000 m, around +5 °C
Wind
Mostly light from southerly directions
Weather forecast to Sunday
Conditions will be sunny and mild in the mountains.
Fresh snow
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Temperature
At midday at 2000 m, between +5 °C in the north and +3 °C in the south
Wind
Mostly light southwesterly to westerly winds
Outlook
On Monday it will be mostly sunny in the mountains, with high broken cloud cover moving in from the southwest in the afternoon. On Tuesday it will mostly be very cloudy with foehn-like bright spells in the east. In the south and on the Main Alpine Ridge in Valais, light precipitation will set in on Tuesday morning, but the precipitation forecast is still uncertain. The southwesterly wind will freshen on Monday and will be moderate to strong. In the alpine valleys on the northern flank of the Alps, there will be moderate to strong southerly foehn winds and it will continue to be mild.
The avalanche danger will increase slightly on Monday during the course of the day with small snowdrift accumulations that are sometimes prone to triggering. On Tuesday, it will increase somewhat in the south during the course of the day with new fallen snow.